Abstract

A fine calibration of the depolarization ratio is
required for a detailed interpretation of lidar-observed polar
stratospheric clouds. We propose a procedure for analyzing data by
using atmospheric depolarization lidar. The method is based on a
plot of δT versus (1 -
RT-1), where
δT is the total depolarization ratio and
RT is the total backscattering
ratio. Assuming that there are only spherical particles in some
altitude ranges of the lidar data, the characteristics of the plot of
δT versus (1 -
RT-1) lead to a simple but effective
calibration method for δT. Additionally,
the depolarization of air molecules δm can be
determined in the process of δT
calibration. We compared determined values with theoretically
calculated values for the depolarization of air to test the proposed
method. The δm value was calculated from
the lidar data acquired at Ny-Ålesund (79 °N, 12 °E),
Svalbard in winter 1994–1995. When only sulfate aerosols were
present on 24 December 1994, δm was 0.46
± 0.35%. When the particles consisted of sulfate aerosols and
spherical particles of polar stratospheric clouds on 4 January 1995,
δm was 0.45 ± 0.07%. Both
δm values were in good agreement with the
theoretically calculated value, 0.50 ± 0.03%.

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